Didumos69

It is because of my diagonal drive project that I am in pursuit of a reliable stepper, but I didn't test whether it generates enough torque to shift back from 4th to 3rd gear. In what sense does it fail? In my setup the output is about as strong as the servo itself. Only little power is needed to push a ratchet aside. In my manual video I show what happens when I block the output: the input is blocked too. What if you test your setup with a servo directly attached to your gearbox?

Yes, it needs to be the differential with 16/24 teeth. A full parts list is available on Rebrickable.

I made instructions during lunch:

No, you cannot. I tried using that part and it locks the differential in two directions; it hooks on to the differantial too low to make enough difference between locking and slipping. There must be other configurations possible, but it all comes very precise. Here are a few requirements that need to be met: After a return, when the differential is idle and locked by both ratchets, the exact position where the ratchets hook on to the differential should be such that one tooth of the 24t side of the differential is pointing straight up. This is needed to get equal starting points for shifts in both directions. The previous shift should not put one direction in favor of the other by leaving a slighlty off-center differential. The 12t gears hook on to the differential at exactly the right height to obtain a properly centered differential after each shift. When the input returns, the open ratchet needs to re-engage with the 24t side of the differential only after the 3rd tooth passes the other ratchet. If the open ratchet re-engages too early, the differential will not return the required 45 degree (3 teeth). To prevent the open ratchet from closing too early, the orange (0X)-piece which controls the ratchets needs to sit tight against the ratchets, even in its centered (idle) position. That way the ratchet will only be fully re-engaged once the (0X)-piece points straight up again. I used the reddish brown 3L axles with stop to bring the ratchet close enough to the (0X)-piece. When the output is blocked, for instance in case of a 4th-to-1st gear lock in a sequential gearbox, the ratchets should not slip, not even when a Servo-motor is used as input. This means an engaged ratchet should really hook on to the differential. The 12t gears do a very good job in that respect. I also tried with a 28t differential and an 8t gear as ratchet, but a 45 degree return would translate into 3.5 teeth, which would practically result in a 3 or 4 teeth return and thus a biased starting point for the next shift.

In pursuit of a reliable two-way 90° stepper that is capable of handling high torque without slipping, I came up with this solution. It has been specifically designed for use with a PF Servomotor, that is for 90° input rotations, clockwise and counterclockwise. How does it work? While idle, the differential housing can't rotate, because it's locked by two ratchets (which lock in one direction and slip in the other direction). The ratchets are tied together with a single white silicon band, only one stud distant from their rotation points (not visible in video). When the input engages, one ratchet opens, but the other ratchet prevents the differential from rotating along with the input axle. The result is that the input flows through the bevel gears inside the differential housing, and outputs with a 1:1 ratio. When the input returns, the 90° limiter prevents the output from returning, forcing the differential to slip over the one ratchet that is still engaged. After returning completely, the open ratchet re-engages and the differential housing is completely locked again. When you listen carefully, the return gives three clicks. The differential housing returns with half the speed of the input axle. This means it will rotate backwards 45°, which covers exactly 3 teeth of the 24-teeth side of the differential. Background It all comes very precise. Here are a few requirements that needed to be met: After a return, when the differential is idle and locked by both ratchets, the exact position where the ratchets hook on to the differential should be such that one tooth of the 24t side of the differential is pointing straight up. This is needed to get equal starting points for shifts in both directions. The previous shift should not put one direction in favor of the other by leaving a slighlty off-center differential. The 12t gears hook on to the differential at exactly the right height to obtain a properly centered differential after each shift. When the input returns, the open ratchet needs to re-engage with the 24t side of the differential only after the 3rd tooth passes the other ratchet. If the open ratchet re-engages too early, the differential will not return the required 45 degree (3 teeth). To prevent the open ratchet from closing too early, the orange (0X)-piece which controls the ratchets needs to sit tight against the ratchets, even in its centered (idle) position. That way the ratchet will only be fully re-engaged once the (0X)-piece points straight up again. I used the reddish brown 3L axles with stop to bring the ratchet close enough to the (0X)-piece. When the output is blocked, for instance in case of a 4th-to-1st gear block in a sequential gearbox, the ratchets should not slip, not even when a Servo-motor is used as input. This means an engaged ratchet should firmly hook on to the differential to keep it put. The 12t gears do a very good job in that respect. I also tried with a 28t differential and an 8t gear as ratchet, but a 45 degree return would translate into 3.5 teeth, which would practically result in a 3 or 4 teeth return and thus a biased starting point for the next shift. Instruction on Rebrickable.

High spin and low torque, that actually summarizes my strategy towards the whole drive-train, it is also my approach to avoiding slipping gears inside the differentials. Currently I use the output of the XL motors to provide two inputs for the gearboxes: One input is geared up by 3:1 and the other input is geared up by 5:3. The outputs of the gearboxes are then geared down by 3:5. So I already have the gearboxes running with relatively high spin / low torque. If I want to have even higher spin and lower torque, I will need to introduce more gear meshes to gear up the XL-motor outputs and also more gear meshes to gear down the transmission outputs. That would make the whole setup much less efficient I fear.

The motors can indeed handle the 3.00 ratio and I could obtain ratios running from 1.00 to 3.00 by skipping the down-gearing in the toggle joints that are part of the front and rear axles. But the problem is that the shifter cannot shift at speed when the ratio comes above 2.2.

@Attika, perhaps it's also good to know the ratios the transmission currently has. The input (directly from the XL-motors) output ratios of the transmission are 0.55, 1.00, 1.65 and 3.00. This is geared down by 0.60 in the toggle joints that are part of the front and rear axles. As you can see, 4th gear is 5.4 times faster than 1st gear, which makes a huge difference. By changing a few gear meshes, I can change the ratios to 0.55, 0.92, 1.00 and 1.65. That would work reliably with the shifter I have now, but the difference between 2nd and 3rd gear would be really small. Guess I have to make up my mind about what's more important; max speed or being able to shift gears at speed? So far I think the latter is more important.

But the 'teeth' of the d-rings and c-gears are straight, so I don't see why they would want to slide out when the friction between d-rings and c-gears is eliminated. I still agree lubrication would not be the most elegant solution. Releasing the throttle for a fraction is undoable. It halts almost immediately.

This is exactly what is going on @Attika. I thought I could make things work by skipping 4th gear in combination with not gearing down the outputs towards the wheels to compensate for the lost max speed. But in that setup the extra torque in 3rd gear gives the exact same problem when shifting back from 3rd to 2nd gear. That confirms your explanation: High torque makes it hard to pull the driving rings out of the clutch gear. Even the setup above, which is really strong, cannot pull the driving ring out of the clutch gear under high torque. The only setup that works, is when I drop 4th gear and hold on to gearing down the outputs towards the wheels, but that drops max speed significantly. In that setup I can reliably shift from 1st to 3rd gear and back. Perhaps lubricating the 'teeth' of the driving rings will make them disengage under high torque more easily?

This is the strongest rendition of my shifter so far, also with the best reach: The shifter now completes a full 90 degree shift, the 90 degree limiter is only necessary for allowing the shifter to return prperly. I hope this will allow me to shift back from 4th to 3rd gear.

Okay, but like you said, we have had a pullback contest last year and one way of dealing with that is to generalize away from the pullback a little. But personally I wouldn't have a problem with another pullback-oriented contest.

I like the idea, but I would drop the mandatory pullback. Just two small models and a third that combines the parts. In other words: a 1+1=3 contest with limited parts.

I appreciate you are trying to experiment with the dd-drive yourself. That's the best way to value it. Thanks @AFOLegofan66! I hope I can live up to the expectations. At this stage I'm actually quite unhappy with the fact that I can't get shifting back from 4th to 3rd gear to work reliably. Still have some ideas to improve things though.

That would be really cool! Thanks for sharing the pictures, the yellow and black make a very nice color combo!

That does not look cool. I suppose this approach requires wider tires.

You're making me curious, but if I remember correctly, something with yellow and black?

So you have 10 of those large shocks ?!

If your RC-tires fit, it could indeed be a nice option for the Greyhound. I saw you don't use the inner tires, so the wheels on your Greyhound must be a bit sloppy now. This would solve that. Can you let me know if the RC tires fit the Porsche rims? Another option would be to put the CLAAS tires on the Porsche rims, but then your tires will probably stretch and will no longer be usable on the CLAAS rims. Btw, I updated the design of these hubs in the mean time, you can find the ldd file here and the stud.io file here. Here you see a cutaway:

This will allow you to remove the bent liftarms:

It all depends on what you define as toy or what you define as playable. Of course the building experience is part of the play, but when building some sophisticated mechanisms results in a model that functions poorly or not at all, much of the joy is taken away. If building would be the only pleasure gained from LEGO then there would be no need for a Technic theme.

That's exactly what it is. And the dual diagonal drive is 1) to divide torque over two separate drive trains while 2) preserving the advantage of having open differentials when cornering and 3) to pass this kind of tests at the same time, even without the differential lock engaged.

Thanks and good to know you're building again. Leaving out the red pins is indeed to make it more easy to take out the Buwizzes. You first need to remove the bent liftarms: 1) first push back the 4L axle with endstop - but not further than necessary - so you can remove the black pieces right in front of the flanks. 2) then remove the red connectors with pin with towballs inserted and 3) finally remove the black pins with axle-hole adjacent to the bent liftarms. Now you should be able to remove the bent liftarms. I'll add some pictures later.

Update: The differential lock is working now and the gear shifter is also working better, but it still has a hard time shifting back from 4th to 3rd gear. So my plan is: I will drop 4th gear and add a 3rd-to-1st gear block instead. I will also drop the down-gearing in the toggle joints at the ends of the drive trains to somewhat compensate for the lost speed in 4th gear. Here are two short videos showing shifting and the differential lock (with some help from my daughter ).

Interesting topic ?. To me LEGO is a toy and 42100 is not. Toys should be playable and over the last few years LEGO is releasing less playable Technic models with less and less reluctance. 42056 and 42083 are signs on that wall and I can't imagine 42100 to be really playable. In my believe, Technic parts - pins, beams, gears, connectors, pf - are not suited for this scale models. Making a stable structure at this scale will make it so heavy that Technic gears and pf are too weak to make it function pleasingly I don't have problems with LEGO walking this path. If it sells, who am I to say they shouldn't. If LEGO is good and perseveres, I'm good. But it's not a toy.